There has for several years been manufactured, by the assignee of applicants, a power resistor having a relatively thick copper base that serves not only as the heatsink but as the structural-support component of the resistor. A portion of this heatsink-base is apertured for mounting by a bolt to the underlying chassis. The remaining portion is indented in comparison to the first-mentioned portion, and has a ceramic substrate bonded thereto. A resistive film is provided on the side of the substrate remote from the heatsink. The film is connected to termination leads by metallization traces and solder. The substrate and the lead ends, and only part of the heatsink-base, are encapsulated in silicone molding compound, in such manner that the bottom surface of the heatsink-base----and the entire heatsink-base in the region of the bolt aperture----are exposed. The bottom heatsink surface is in flatwise contact with the chassis.
It has now been discovered that a power resistor having a vastly higher power rating than that of the resistor described above can be manufactured at less cost, and with strength adequate for the great majority of applications, although not as much strength as that of the above-indicated resistor incorporating relatively thick metal.
The power rating of the present resistor is at least double that of the earlier one referred to in the preceding paragraphs, yet the overall area of the present resistor (bottom surface) is less than 14% higher than that of the earlier one. The cost per watt of power rating of the present resistor is about one-half that of the earlier resistor referred to in the preceding paragraphs, in that there is less copper and less difficulty of assembly.